1. Field of the Invention
This invention relates to a slip control system for a vehicle, and more particularly to a slip control system for a vehicle in which the slip control is effected during turning taking into account the difference in the rotational speed between the inner driving wheel and the outer driving wheel.
2. Description of the Prior Art
There has been put into practice a traction control system which detects the amount of slip of the driving wheels and controls the engine output and/or application of braking force to the wheels so that the amount of slip of the driving wheels converges on a target value, thereby preventing deterioration of acceleration of the vehicle due to an excessive driving torque transmitted to the driving wheels. Many vehicles are provided with a traction control system as well as an anti-skid brake system. See, for instance, Japanese Unexamined Patent Publication No. 1(1989)-197160.
When the vehicle is making a turn, the wheel speed of the outer driving wheel becomes higher than that of the inner driving wheel and accordingly the apparent amount of slip of the outer driving wheel becomes larger. It is not preferred that the slip control is effected on the basis of the large apparent amount of slip.
In Japanese Unexamined Patent Publication No. 62(1987)-60937, there is disclosed a traction control system in which the detected amount of slip is corrected taking into account the difference in the rotational speed between the inner driving wheel and the outer driving wheel during turning.
When the detected amount of slip is corrected taking into account the difference in the rotational speed between the inner driving wheel and the outer driving wheel, an ideal radius of turn is first calculated on the basis of the steering angle detected by a steering angle sensor and the detected amount of slip is corrected on the basis of the ideal radius of turn. However since the actual turning behavior of the vehicle is slightly behind the change in the detected steering angle, there arises a problem that the correction of the detected amount of slip can be effected prematurely before the actual behavior of the vehicle.